WASHINGTON (AP) ' U.S. counterterrorism officials are chasing an unconfirmed al-Qaida (al-KAH'-ee-duh) threat to attack New York or Washington in a plot timed to coincide with the 10th anniversary of the Sept. 11 attacks.

Officials said the intelligence came in late Wednesday night and indicated al-Qaida planned to use car bombs to blow up bridges or tunnels in New York or Washington. The information also led intelligence officials to believe that there were three individuals involved who were either in the U.S. or planned to travel here.

The threat is being described as specific and credible but unconfirmed.

Security has been ramped up around the country in the weeks leading up to the 10th anniversary, a date officials have long known al-Qaida viewed as an appealing time to attack.